Bifocal-lens blank



H. J. STEAD BIFOCAL LENS BLANK Feb. 5, 1924;

Filed March 23. 1921 i 15, nished'to thetrade circularfield canw vature, and"Will-Iiotrequire additional labor such as grinding and polishing In order tov Patented Feb 5,1924}; I

mason) x. mm, or GENEVA, new xonx.

curios.

airman-anus BLANK.

To all whomit may concern:

' Be it known that I, HAROLD J. em, a citizen of; the United States of Geneva, in the county of Ontario, in the State of New 5 York, have invented new and useful Improvemen-ts in Bifocal-Lens Blanks, of which the. following, taken in connection with the accompanying drawings, is a full, clear, and

- exact description. i

l0 This invention relates to certain improvements in bifocal lens blanks and the tools and process for producing the same.

So far as Tam aware, practically all commercial onepiec'e bifocal. lens blanks furembody two ground and polished optical-.fieldsof different dioptrics'upon one. side ofa piece of glass.

It will be obvious that with a blank of a that character in which the relation of the bifpcal surfaces isfixed as to curvature, the prescription lens grinder, in'order to' pro,-

' duce the mult1tu e of prescriptions pre-.

- scribed for various degrees' of eye defects,- .must have a large stock of blanks in which the relative curvature of the bifocal surfaces large quantity of the rough side.

difien-and must have a grinding tools for finishing of the blank.

These tools usually have" a different curve, or combination of curves, which in combination with the already finished side of the bifocal blank, form a finished lens ac cording to prescription. V These tools cost approximately $1.00 each,

and ,thereare upwardlyof three hundred: of

; them'require'd to produce the general runof.

There would be an infinitely of theinrequired to fill all thousands of lens come prescriptions. large number prescriptions :(many binations "essential to the finishing ofvthe present onepiece bifocal'blank has seriously retards the commercial development of that prod.

uct.

only finished. Thisreading field, or section,

ailarge lens blank, and is the surrounding surface.- have demonstratedthat arelatively small be molded .to accurate cur adapt perfectly for visual purposes.

'of a bifocal lens blank, he may do so finish to prescription'by grinding both sides toany focal power use. A I

With the central or reading'section mold-v now in general use.

when a required prescription is presented. C astep in production, distance surface to any pre-determined curvature' desired-. .The only precaution necesand theffact that these tools are d with which the being ground. This necessarily would form invention consists primarily ill- 3; bi focal lens .blank ha'ving the reading field in diameter, an.

. each Application filed march 28, 1921. Serial ml 454,627.

distance section rough and the opposite side of the blank rough, a tremendous saving is eflected not only .as to the original equip inent required by the dealer, but also a sav ing in constant up-keep. This together with the small number of blanks which the dealer would be required to carry in stock covering a certain range of r Y considerable to-the dealer. When the dealer is ready to grind, or does grind both sides with f the ordinary grinding tools in common use.

Therefore, it is an extreme advantage to give to the dealer a that might be calledfor, with the ordinary grinding tools in common ed perfectly, the outer section is then ground and polishedin the usual manner with ordinaryv lens-grinding achinery, and the tools This work can be done by the dealer,

Or the manufacturer'may, as "grind this outer," or

s'ary in perform'ng that operation is not to grind too far so that the central or reading field would be'touched by the grindingtool 'outer. or distance surface is a 'VBIlilCfil shoulder separating the reading.

and distance fields, which shoulder would .Vary

in heightin different prescriptions, according to the difi'erence 1n curvature between these two fields.

lens prescriptions, means bifocal blank which he can The blank so formed with the readingsec; 1

tion molded toyan' accurate curvature, may,

d the moulded reading field maybe approximately '32 mm. in diameter, permitting "the lens blank to be cut in half,

half forming a single as illustrated, be approximately three inches bifocal lens.- 0

However, preferably the reading Section would be formed about 19 mm. in diameter, and a. single lens blank would be cut from the large blank in such. manner that the 19 mm. readin the blank w en cut out.

This depressed reading field may be molded upon either the concave or convex side of the blank, and the balance of the blank is left rough, so that the dealer can finish it as he wishes with the ordinary tools commonly used in lens grinding establishments.

Other objectsand advantages of the invention will more fully appear from the following description, taken in connection with the accompanying drawings, in which: c

Figure 1 is a sectional view of a mold secti'onand a glass blank supported thereby.

Figure 2 is a similar section after the glass has conformed itself to the mold section. a

Figure 3 isa section illustrating the method of'moldingthe bifocal side of the blank. I

Figure 4: is a face view of the completed blank.

V Figure 5 is a modification of themold,

' showing the bifocal surfaces as molded upon the concave side of the blank.

The surface of the glass blank 1' upon which the reading field is to bemolded should first be polished. It is not necessary to polish the entire surface, but only that portion which is to form the reading surface. This surface is then thoroughly cleansed and rendered free from all foreign material, and is placed on a form or mold, section .2., which may be composed of any suitable refractory substance that will impart ,to the glass the general curvature required on the side of the blank opposite the bifocal side.

The blank is covered with any suitable cover, as a porcelain cover, or one made of any material which will not oxidize or scale and permit falling particles-to drop upon the surface 0f-.the glass which is to form the reading field. This assembly, includingthe mold section 2, the glass blank land the suitable cover, is placed in a furnace,

heated in. any suitable manner, as by gas \OI electricity, and to a temperature suflicient to heat and cause the glass to subside and conform generally to the mold section upon which it is resting.

7 from the furnace, the glass blank 1- un- .surface thereof into a counterpart of the die,

or old section 3.

he mold sections 2'- and --3 formfield would be at one edge of When the glass has reached a proper mold ing temperature, the assembly is withdrawn.

meaeeo and which is to be molded to an accurate curvature, should be of a material which is of infinitely fine grain or texture, and that will accept on its surface a very high finish or polish substantially the same as glass. This is necessary so that the surface of the glass formed by this mold section shall be an exact counterpart of the surface of this part of the mold itself. For this; purpose the mold section -3- is preferably formed in two parts. Q

The main portion of the same, and which is adapted to shape the distance field of the blank to a'generally accurate curvature is of annular form, and may, as heretofore stated,

be "formed of cast-iron or other suitable material. A section 5adapted to mold the reading field to an accurate curvature is remo vably inserted within the central recess of the annular body ,6- of themold section 3.. This part 5 is of such size andform as to tightly fit within the annular part 6 and preferably projects somewhat below the molding surface of the part 6 so that the reading field when molded by the mold section 3 lies below the surface of the distance portion of the blank as molded by the annular part 6. In other words, thereading field, when completed, is depressed beneath the general contour of the blank. This permits the distance field 8. .of the blank to be ground by the ordinary grinding tools without special precaution, care being taken only to stop the grinding of the distance field before the grinding tool comesinto contact .with the depressed reading surface 9 The glass so molded is then placed in an oven and subjected to' an'increased temperature to fire polish the'surface of the readin section, Then the blank is gradually coole That part of the mold forming the reading sectioirmay be changed from time to time according to the curvature desired to secure difl'erent bifocal additions p In Figure 4 the comple'tedblank is shown and the circle 7 indicates the commercial blank to be cut therefrom. However, as

above stated, the reading surface may be of suflicient diameter to permit its utilization in the formation of two bifocal lens blanks; This will be effected blank when completed and utilizing each half in the manufacture of a single lens.

In Figure 5 a reverse condition is shown in that the reading field is molded upon the concave side of the blank. n other respects the construction is the same. f

by merely splitting the It is essential that the part 5 of the mold may neeaeeo section 3 should be formed of a suitable material so as to produce an accurately molded surface which will not require subsequent grinding or polishing.

I have found that the metal nickel and the alloys known as Monel and Invar are suitable for my purpose. However, there be various other materials equally as well suited and perhaps more efiicient for the purpose, and I do not desire to limit myself to these particular substances for the formation of the die parts to shape the reading field. Further, when desired, the entire mold section -3- may be formed of one integral piece of the metal such as nickel found most satisfactory for molding the blank to accurate curvature suitable for visual purposes without grinding or polishing in the usual manner. Altho it may be desirable in certain cases to slightly polish the surface after molding and by finished visual surface, as used in the claims of this application, I mean such a molded surface as is suitable for visual or optical purposes without additional grinding, altho some polishing may be desirable.

Although I have shown and described a specific form and construction of lens blank, and have set forth in detail a perhaps preferred method of manufacturing the same, I do not desire to limit myself to the details of either the product or the process except as the same may be specifically set forth in the claims hereto appended.

What I claim is:

1. 'A lens blank having upon one face a relatively small depressed central portion molded to an accurate curvature suitable for visual purposes without grinding or polishing, and a relatively large surrounding surface molded to an approximate curvature,

and the other face of the blank molded to an approximate curvature.

2.'A lens blank having upon one face a relatively small portion molded to an accurate curvature suitable for visual purposes without grinding or polishing, and a relatively large portion shaped to an approximate curvature and surrounding the relatively small portion.

3. A bifocal lens blank having a relatively small center portion molded to an accurate curvature suitable for visual purposes without grinding.

4. A bifocal lens consisting of a piece of ished to an accurate curvature, surface having a distance field ground and polished to an accurate curvature and a near eld molded to an accurate curvature and separated from the distance field by an intervening shoulder.

5. A bifocallens having a near field molded to an acburate curvature suitable for visual purposes without grinding, and depressed beneath the adjacent field.

6. A bifocal lens consisting of a piece of glass having one surface ground and polished to an accurate curvature, the opposite surface having a distance field ground and polished to an accurate curvature and a near lass having one surface ground and pol-' the oppositeeld molded to an accurate-curvature suitable for visual purposes without grinding.

7. A bifocal lens blank having a relatively small portion molded "to an accurate curvature sultable for forming the near vision portion of a bifocal lens without grinding,

and a comparativelylarge adja-f' cent integral portion adapted to form the distance" vision portion of said bifocal lens.

8. A bifocal lens blank having a relatively small curvature suitable for forming the near vision portion of a bifocal lens without grinding, and a comparativelylarge adjaportion molded to an accurate cent integral portion adapted .to form the distance vision portion of said bifocal lens, the latter portion being raised above the former.

9. A bifocal lens blank having a relatively smallportion molded to an accurate curvature suitable for visual purposes with out grinding, and an adjacent integral portion of larger size adapted to form the .distance visual portion of a bifocal lens.

In witness whereof I have hereunto set my hand this 10th day of Mch. 1921.

H. E. CnAsn, 11 A. 'Inomrson. 

